alarm

Arranges to have a SIGALRM delivered to this process after the
specified number of wallclock seconds has elapsed. If SECONDS is not
specified, the value stored in $_ is used. (On some
machines, unfortunately, the elapsed time may be up to one second less
or more than you specified because of how seconds are counted, and
process scheduling may delay the delivery of the signal even further.)

Only one timer may be counting at once. Each call disables the
previous timer, and an argument of 0
may be supplied to cancel the
previous timer without starting a new one. The returned value is the
amount of time remaining on the previous timer.

For delays of finer granularity than one second, the Time::HiRes module
(from CPAN, and starting from Perl 5.8 part of the standard
distribution) provides
ualarm .
You may also use Perl's four-argument version of
select leaving the first three
arguments undefined, or you might be able to use the
syscall interface to access setitimer(2)
if your system supports it. See perlfaq8 for details.

It is usually a mistake to intermix alarm and
sleep calls, because sleep may be
internally implemented on your system with alarm.

If you want to use alarm to time out a system call
you need to use an eval/die pair. You
can't rely on the alarm causing the system call to fail with
$! set to EINTR
because Perl sets up signal handlers
to restart system calls on some systems. Using
eval/die always works, modulo the
caveats given in Signals in perlipc.